Belt unit and image forming apparatus

ABSTRACT

A belt unit is provided with an endless belt, a driving roller, and a pair of guide ribs. The driving roller is disposed on an inner peripheral surface side of the endless belt and drives the endless belt. The pair of guide ribs is placed on each opposite widthwise end of the inner peripheral surface of the endless belt and contacts both end faces of the driving roller, thus preventing meandering of the endless belt. Additionally, the driving roller is equipped with a low friction region at both opposite lengthwise ends in a predetermined width and the low friction region is configured to have a friction coefficient that is lower than a friction coefficient of a region adjacent to the low friction region.

CROSS REFERENCE

This Nonprovisional application claims priority under 35 U.S.C. §119(a)on Patent Application No. 2011-252453 filed in Japan on Nov. 18, 2011,the entire contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

The present invention relates to a belt unit capable of enhancing themeandering prevention of an endless belt and also to an image formingapparatus equipped with the belt unit.

Conventionally, as driving rollers that drive an endless belt used forequipment such as OA (Office Automation) equipment, is for example,driving rollers that include a roller body and elastic rubber that woundaround the surface of the roller body had been known.

In recent years, however, improvement in the speed and colorization ofcopying machines, laser beam printers (LBP), and the like has beendeveloped, so that the above mentioned driving rollers with the endlessbelt, due to the variation in the speed of feeding the endless belt bythe driving roller and the irregularities of the surface of the endlessbelt, have problems such as character skew, image stretch, and colordeviation. Thus, the dimensional precision of the driving roller and thedriving precision of the belt have been very crucial.

In an attempt to solve such problems, as the driving rollers for the OAequipment, driving rollers that include sponge-typed elastic rubber thatis wound around the roller body have been disclosed (see JapaneseLaid-Open Patent Publication 2010-152063, for example).

However, in Japanese Laid-Open Patent Publication 2010-152063, a guiderib disposed in the endless belt is likely to overrun on the drivingroller for an extended time. This is because the whole externalperipheral surface of the driving roller disclosed in Japanese Laid-OpenPatent Publication 2010-152063 is wound with sponge typed elastic rubberand the elastic rubber is entirely made of a material having a highfriction coefficient.

In view of the problem described above, an object of the presentinvention is to provide a belt unit that can prevent a guide rib fromoverrunning on a driving roller for an extended time.

SUMMARY OF THE INVENTION

A belt unit of the present invention is provided with an endless belt, adriving roller, and a pair of guide ribs.

The driving roller is disposed on an inner peripheral surface side ofthe endless belt and drives the endless belt. The pair of guide ribs isplaced on each opposite widthwise end of the inner peripheral surface ofthe endless belt and contacts both end faces of the driving roller, thuspreventing meandering of the endless belt. Additionally, the drivingroller is equipped with a low friction region at both oppositelengthwise ends in a predetermined width and the low friction region isconfigured to have a friction coefficient that is lower than a frictioncoefficient of a region adjacent to the low friction region.

With this configuration, even if the guide ribs overrun on the drivingroller, since the frictional force generated between the guide ribs anda low friction region is small, the guide ribs return to a position inwhich each of the guide ribs contacts an end face of the driving rollerby sliding toward the end face of the driving roller. Therefore, theguide ribs can be is prevented from overrunning on the driving rollerfor an extended time.

The foregoing and other features and attendant advantages of the presentinvention will become more apparent from the reading of the followingdetailed description of the invention in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view of a configuration of an image forming apparatusthat is equipped with a secondary transfer belt unit according to afirst embodiment of the present invention;

FIG. 2 is a front view of a configuration of the secondary transfer beltunit according to the first embodiment of the present invention;

FIG. 3 is a side elevational view of the configuration of the secondarytransfer belt unit according to the first embodiment of the presentinvention;

FIG. 4 is a side elevational view of a configuration of a secondarytransfer belt unit according to a second embodiment of n the presentinvention;

FIG. 5 is a sectional side elevational view of the configuration of thesecondary transfer belt unit according to the second embodiment of thepresent invention;

FIG. 6 is a side elevational view of a configuration of is the secondarytransfer belt unit according to a third embodiment of the presentinvention;

FIG. 7 is a side elevational view of a configuration of a driving rollerof a secondary transfer belt unit according to a fourth embodiment ofthe present invention;

FIG. 8 is a side elevational view of the configuration of the secondarytransfer belt unit according to the fourth embodiment of the presentinvention;

FIG. 9 is a sectional side elevational view of the configuration of thesecondary transfer belt unit according to the fourth embodiment of thepresent invention;

FIG. 10 is a side elevational view of a configuration of a secondarytransfer belt unit according to a fifth embodiment of the presentinvention;

FIG. 11 is a side elevational view of the configuration of the secondarytransfer belt unit according to the fifth embodiment of the presentinvention;

FIG. 12 is a side elevational view of the configuration of the secondarytransfer belt unit according to the fifth embodiment of the presentinvention; and

FIG. 13 is a side elevational view of the configuration of the secondarytransfer belt unit according to the fifth embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, a belt unit according to an embodiment of the presentinvention will be described in detail with reference to the drawings.

To begin with, description will be made of a first embodiment of thepresent invention.

FIG. 1 is a front view of a configuration of an image forming apparatus10 that is equipped with a secondary transfer belt unit 40 according tothe first embodiment of the present invention.

The image forming apparatus 10 is provided with a plurality of imageforming portions 20A, 20B, 20C, and 20D, a primary transfer unit 30, asecondary transfer belt unit 40, a fixing unit 51, a paper feed path 52,a sheet feed cassette 53, a manual feed tray 54, a paper output tray 55,and a control portion 60. The control portion 60 controls each part ofthe image forming apparatus 10 in an integrated manner.

The image forming apparatus 10 carries out an electrophotographic imageforming process using image data corresponding to four colors: black andthe three subtractive primary colors, that is, cyan, magenta and yellow,obtained by color separation of a color image. The image formingportions 20A to 20D are configured to form toner images (developerimages) of the respective colors. The image forming portions 20A to 20Dare horizontally arranged in a row along the primary transfer unit 30.

The following description is directed mainly to the image formingportion 20A. The other image forming portions 20B to 20D aresubstantially similar in configuration to the image forming portion 20A.The image forming portion 20A, which is associated with black, includesa photoreceptor drum 21A, a charger device 22A, an exposure device 23A,a developing device 24A, and a cleaning unit 25A and is configured toform a black toner image by the electrophotographic image formingprocess.

The photoreceptor drum 21A and photoreceptor drums 21B, 21C, and 21Dwith which the image forming portions 20B to 20D are provided, arerotated in one direction by a driving force transmitted from anon-illustrated driving motor. The photoreceptor drum 21A is an imagebearing element for monochromatic images, and the photoreceptor drums21B to 21D are image bearing elements for color images.

The charger device 22A is disposed as opposed to the peripheral surfaceof the photoreceptor drum 21A and configured to charge the peripheralsurface of the photoreceptor drum 21A to a predetermined potential.

The exposure device 23A is configured to irradiate the n peripheralsurface of the photoreceptor drum 21A with a laser beam modulatedaccording to black image data. By such irradiation, an electrostaticlatent image according to the black image data is formed on theperipheral surface of the photoreceptor drum 21A.

The developing device 24A stores black toner (developer). The developingdevice 24A supplies the toner to the peripheral surface of thephotoreceptor drum 21A to develop the electrostatic latent image into atoner image.

The developing devices 24B to 24D of respective of the other imageforming portions 20B to 20D store cyan toner, magenta toner, and yellowtoner, respectively, and the photoreceptor drums 21B to 21D of therespective image forming portions 20B to 20D are configured to form acyan toner image, a magenta toner image, and a yellow toner image,respectively.

The primary transfer unit 30 has a primary transfer belt 31, a primarytransfer driving roller 32, a primary transfer driven roller 33, primarytransfer rollers 34A to 34D, and an primary transfer belt cleaning unit35.

The primary transfer belt 31 is in the form of an endless belt and isstretched over the primary transfer driving roller 32 and the primarytransfer driven roller 33 to move around the driving and driven rollersin a predetermined direction. The outer peripheral surface of theprimary transfer belt 31 is opposed to the photoreceptor drums 21A to21D of the respective image forming portions 20A to 20D.

The primary transfer rollers 34A to 34D are positioned as opposed to therespective photoreceptor drums 21A to 21D with the primary transfer belt31 held between the rollers and drums. The region in which the outerperipheral surface of the primary is transfer belt 31 is opposed to thephotoreceptor drums 21A to 21D is a primary transfer region.

The cleaning unit 25A is configured to collect residual toner remainingon the peripheral surface of the photoreceptor drum 21A after theprimary transfer following the developing step.

The secondary transfer belt unit 40 is configured to be capable ofcontacting and separating from the primary transfer driving roller 32with the primary transfer belt 31 held between the unit and the belt.The region in which the primary transfer belt 31 and the secondarytransfer belt unit 40 are pressed against each other is a secondarytransfer region.

The photoreceptor drums 21A to 21D are disposed, from a direction closerto the secondary transfer region, in the order of the photoreceptor drum21A for black, the photoreceptor drum 21B for cyan, the photoreceptordrum 21C for magenta, and the photoreceptor drum 21D for yellow. Thetoner image born on the outer surface of the primary transfer belt 31 isfed to the secondary transfer region as the primary transfer belt 31 ismoved.

The sheet feed cassette 53 stores sheets. On the manual feed tray 54,non-standard size sheets or thick paper sheets are placed. The sheetfeed path 52 is configured to guide each of the sheets fed from thesheet feed cassette 53 or the manual feed tray 54 to the paper outputtray 55 via the secondary transfer region and the fixing unit 51.

A registration roller 56 is disposed near the upstream side of thesecondary transfer region in the sheet feed direction. The sheet fedfrom the sheet feed cassette 53 or the manual feed tray 54 to the paperfeed path 52 comes to abut against the registration roller 56 in astationary state, so that the direction of the sheet is corrected, andis supplied to the secondary transfer region by the registration roller56 that starts rotating at a predetermined timing. The sheet thus fedinto the secondary transfer region is brought into intimate contact withthe primary transfer belt 31.

A predetermined secondary transfer electric field is formed in asecondary transfer region, so that the toner image born on the primarytransfer belt 31 is secondarily transferred to the sheet.

The primary transfer belt cleaning unit 35 collects residual toner ofthe toner born on the primary transfer belt 31 that remains on theprimary transfer belt 31 without having been transferred to the sheet.This prevents color mixture from occurring in the subsequent steps.

The fixing unit 51 has a heating roller 511 and a pressure roller 512.The heating roller 511 and the pressure roller 512 are pressed againsteach other. The fixing unit 51 heats and pressurizes the sheet byholding the sheet with a nip portion between the heating roller 511 andthe pressure roller 512 and is feeding the sheet, thereby firmly fixingand fusing the toner image to the sheet. The sheet on which the tonerimage thus fixed and fused is output to the paper output tray 55 by apair of paper output rollers 57.

FIG. 2 is a front view of a configuration of the secondary transfer beltunit 40 according to the first embodiment of the present invention. FIG.3 is a side elevational view of the configuration of the secondarytransfer belt unit 40 according to the first embodiment of the presentinvention.

The secondary transfer belt unit 40 is provided with a secondarytransfer belt 410, a driving roller 420, a pair of guide ribs 430, and asecondary transfer roller 460.

The secondary transfer belt 410 is an endless belt that is stretchedover the driving roller 420 and the secondary transfer roller 460, andforms a nip portion between the primary transfer belt 31 and thesecondary transfer belt 410. The driving roller 420 is disposed on theinner peripheral surface side of the secondary transfer belt 410 anddrives the secondary transfer belt 410. The pair of guide ribs 430 isdisposed at opposite widthwise ends of the inner peripheral surface ofthe secondary transfer belt 410 and prevents the secondary transfer belt410 from meandering by contacting opposite end faces of the drivingroller 420.

The secondary transfer roller 460 may be disposed as opposed to theprimary transfer belt 31 that contacts the is secondary transfer belt410 and has a surface on which a toner image is formed. In addition, thesecondary transfer roller 460 may preferably transfer the toner imagethat is formed on the primary transfer belt 31 to a sheet that reaches aposition in which the secondary transfer belt 410 and the primarytransfer belt 31 contact each other.

The driving roller 420 is configured to provide a predeterminedwidthwise low friction region 440 at opposite lengthwise ends, and thelow friction region 440 has a friction coefficient that is lower than afriction coefficient of a region 450 adjacent to the low friction region440.

As an example of such measures, as shown in FIG. 3, the base surface ofthe driving roller 420 is exposed as the low friction region 440, andthe base surface of the driving roller 420 is knurl processed in theregion 450. With this configuration, the low friction region 440 isconfigured to have a friction coefficient that is lower than a frictioncoefficient of a region 450.

With this configuration, even if the guide ribs 430 overrun on thedriving roller 420, since the frictional force generated n between theguide ribs 430 and a low friction region 440 is small, the guide ribs430 return to a position in which each of the guide ribs 430 contacts anend face of the driving roller 420 by sliding toward the end face of thedriving roller 420. Therefore, the guide ribs 430 can be prevented fromoverrunning on the driving roller 420 for an extended time.

Subsequently, description will be made of a second embodiment of thepresent invention. In the second embodiment and the embodimentssubsequent thereto, description of features common to the firstembodiment is properly omitted to avoid duplication.

FIG. 4 is a side elevational view of the configuration of the secondarytransfer belt unit 40 according to the second embodiment of the presentinvention. FIG. 5 is a sectional side elevational view of theconfiguration of the secondary transfer belt unit 40 according to thesecond embodiment of the present invention.

The secondary transfer belt unit 40 may preferably include elasticrubber 470. The elastic rubber 470 is wound around an outer peripheralsurface (a region 450) other than the low friction region 440 of thedriving roller 420. In addition, the elastic rubber 470 has a frictioncoefficient that is higher than the friction coefficient of the lowfriction region 440.

Thus, by winding the elastic rubber 470 around the driving roller 420,as shown in a dashed line area 42, an uneven level is created betweenthe driving roller 420 and the elastic rubber 470.

With this configuration, since the elastic rubber 470 need only beattached by winding around the cylindrical driving roller 420, thesecondary transfer belt unit 40 can be easily is manufactured.

Moreover, with this configuration, since the frictional force generatedbetween the secondary transfer belt 410 and the driving roller 420 islarger than the frictional force generated between the secondarytransfer belt 410 and the elastic rubber 470, the holding power of thesecondary transfer belt 410 increases, which can improve the drivingaccuracy of the secondary transfer belt 410.

Furthermore, with this configuration, even if the guide ribs 430 overrunon the driving roller 420, since the frictional force generated betweenthe guide ribs 430 and a low friction region 440 is small, the guideribs 430 return to a position in which each of the guide ribs 430contacts an end face of the driving roller 420 by sliding toward the endface of the driving roller 420. Therefore, the guide ribs 430 can beprevented from overrunning onto the driving roller 420 for an extendedtime.

Additionally, with this configuration, even if the guide ribs 430overrun on the driving roller 420, since the guide ribs 430 slide towardthe end faces of the driving roller 420, the guide ribs 430 are unlikelyto contact the elastic rubber 470, thus preventing the elastic rubber470 from being shaved.

Subsequently, description will be made of a third embodiment of thepresent invention.

FIG. 6 is a side elevational view of the configuration of the secondarytransfer belt unit 40 according to the third is embodiment of thepresent invention.

The secondary transfer belt unit 40 may preferably include elasticrubber 470. The elastic rubber 470 may preferably be wound around theentirety of the outer peripheral surface of the driving roller 420.Additionally, the elastic rubber 470 has a first region 480corresponding to the low friction region 440 of the driving roller 420and a second region 490 corresponding to all other regions: the firstregion 480 is mirror finished and the second region 490 has a frictioncoefficient that is higher than a friction coefficient of the firstregion 480.

Thus, by winding the elastic rubber 470 around the entirety of thedriving roller 420, no uneven level is created in the entirety of thedriving roller.

With this configuration, since the elastic rubber 470 need only beattached by winding around the cylindrical driving roller 420, thesecondary transfer belt unit 40 can be easily manufactured.

Moreover, with this configuration, since the frictional force generatedbetween the secondary transfer belt 410 and the driving roller 420 islarger than the frictional force generated n between the secondarytransfer belt 410 and the elastic rubber 470, the holding power of thesecondary transfer belt 410 increases, which can improve the drivingaccuracy of the secondary transfer belt 410.

Furthermore, with this configuration, even if the guide is ribs 430overrun on the driving roller 420, since the frictional force generatedbetween the guide ribs 430 and a low friction region 440 is small, theguide ribs 430 return to a position in which each of the guide ribs 430contacts an end face of the driving roller 420 by sliding toward the endface of the driving roller 420. Therefore, the guide ribs 430 can beprevented from overrunning onto the driving roller 420 for an extendedtime.

Subsequently, description will be made of a fourth embodiment of thepresent invention.

FIG. 7 is a side elevational view of a configuration of the drivingroller 420 in the secondary transfer belt unit 40 according to thefourth embodiment of the present invention. FIG. 8 is a side elevationalview of the configuration of the secondary transfer belt unit 40according to the fourth embodiment of the present invention. FIG. 9 is asectional side elevational view of the configuration of the secondarytransfer belt unit 40 according to the fourth embodiment of the presentinvention.

The driving roller 420 may preferably have a recessed portion on theouter peripheral surface (a region 450) other than the low frictionregion 440, the recessed portion having a volume equal to the elasticrubber 470. The elastic rubber 470 may also be wound around the recessedportion of the driving roller 420. The low friction region 440 of thedriving roller 420 may be configured to have an external diameter thatis is identical to an external diameter of a region of the elasticrubber in a state in which the driving roller is wound with the elasticrubber 470.

Thus, by winding the elastic rubber 470 around the driving roller 420,as shown in a dashed line area 43, no uneven level is created betweenthe driving roller 420 and the elastic rubber 470.

With this configuration, the elastic rubber 470 is wound around therecess portion of the driving roller 420 and the elastic rubber 470 ispositioned in the recess portion, which improves intimate contactbetween the driving roller 420 and the elastic rubber 470.

In addition, with this configuration, since the frictional forcegenerated between the secondary transfer belt 410 and the driving roller420 is larger than the frictional force generated between the secondarytransfer belt 410 and the elastic rubber 470, the holding power of thesecondary transfer belt 410 increases, which can improve the drivingaccuracy of the secondary transfer belt 410.

Furthermore, with this configuration, even if the guide ribs 430 overrunon the driving roller 420, since the frictional force generated betweenthe guide ribs 430 and a low friction region 440 is small, the guideribs 430 return to a position in which each of the guide ribs 430contacts an end face of the driving roller 420 by sliding toward the endface of the driving is roller 420. Therefore, the guide ribs 430 can beprevented from overrunning onto the driving roller 420 for an extendedtime.

Additionally, with this configuration, even if the guide ribs 430overrun on the driving roller 420, since the guide ribs 430 slide towardthe end faces of the driving roller 420, the guide ribs 430 are unlikelyto contact the elastic rubber 470, thus preventing the elastic rubber470 from being shaved.

Subsequently, description will be made of a fifth embodiment of thepresent invention.

FIG. 10 to FIG. 13 are side elevational views of the configuration ofthe secondary transfer belt unit 40 according to the fifth embodiment ofthe present invention.

Thus, by providing the low friction region 440 in a region other thanboth opposite lengthwise ends of the driving roller 420, the frictioncoefficient of the region 450 adjacent to the low friction region 440can be made higher than the friction coefficient of the low frictionregion 440.

With this configuration, even if the guide ribs 430 overrun on thedriving roller 420, since the frictional force generated between theguide ribs 430 and a low friction region 440 is small, the guide ribs430 return to a position in which each of the guide ribs 430 contacts anend face of the driving roller 420 by sliding toward the end face of thedriving roller 420. Therefore, the guide ribs 430 can be prevented fromoverrunning on the driving roller 420 for an extended time.

It is to be noted that, as shown in the first to the fifth embodimentsof the present invention, the width of the low friction region 440 maypreferably be set to a width not less than the half of the width of theguide rib 430. This configuration allows consistent recovery of thesecondary transfer belt 410 in a case in which the secondary transferbelt 410 meanders.

Finally, the above described embodiments are to be considered in allrespects as illustrative and not restrictive. The scope of the presentinvention is defined not by above described embodiments but by theclaims. Further, the scope of the present invention is intended toinclude all modifications that come within the meaning and scope of theclaims and any equivalents thereof.

What is claimed is:
 1. A belt unit comprising: an endless belt; adriving roller that is disposed on an inner peripheral surface side ofthe endless belt and drives the endless belt; and a pair of guide ribsthat is placed on each opposite widthwise end of the inner peripheralsurface of the endless belt and contacts both end faces of the drivingroller, thus n preventing meandering of the endless belt, wherein: thedriving roller is equipped with a low friction region at both oppositelengthwise ends in a predetermined width; and the low friction regionhas a friction coefficient is that is lower than a friction coefficientof a region adjacent to the low friction region.
 2. The belt unitaccording to claim 1, further comprising elastic rubber that is woundaround an outer peripheral surface of a region other than the lowfriction region of the driving roller, wherein the elastic rubber has afriction coefficient that is higher than the friction coefficient of thelow friction region.
 3. The belt unit according to claim 1, furthercomprising elastic rubber that is wound around an entirety of the outerperipheral surface of the driving roller, wherein: the elastic rubberhas a first region corresponding to the low friction region and a secondregion corresponding to all other regions; the first region is mirrorfinished; and the second region has a friction coefficient that ishigher than a friction coefficient of the first region.
 4. The belt unitaccording to claim 2, wherein: the driving roller has a recessed portionon the outer peripheral surface of the region other than the lowfriction region, the recessed portion having a volume equal to theelastic rubber; the elastic rubber is wound around the recessed portionof the driving roller; and the low friction region of the driving rollerhas an external diameter that is identical to an external diameter of aregion of the elastic rubber in a state in which the driving roller iswound with the elastic rubber.
 5. The belt unit according to claim 1,further comprising: a secondary transfer roller that is disposed asopposed to a primary transfer belt contacting the endless belt andhaving a surface on which a toner image is formed, wherein: thesecondary transfer roller transfers the toner image that is formed onthe primary transfer belt, onto a sheet that reaches a position in whichthe endless belt contacts the primary transfer belt.
 6. An image formingapparatus comprising: the belt unit according to claim 1; and a fixingunit that is disposed on a downstream side from the belt unit and fixeson a sheet a toner image that is transferred onto the sheet by the beltunit.